The present invention relates to fiber optic cables and, more particularly, to water absorbent features of fiber optic cables.
Fiber optic cables include optical fibers which transmit information in cable television, computer, power, and telephone systems. A fiber optic cable may be installed in an environment where the cable is exposed to water. The migration of water in a fiber optic cable is a problem which may occur where the cable jacket has been cut or otherwise breached and water enters the cable. The migration of water in a cable may cause the flooding of a cable passageway or enclosure, and/or it may negatively affect the performance of the optical fibers.
To block the flow of water in a cable, known fiber optic cables may include hardened resin walls, a hard to remove and messy flooding or filling compound, or a more craft-friendly, dry water absorbent chemical. U.S. Pat. No. 4,381,140 discloses a slotted core type fiber optic cable wherein optical fibers are fixed to the slotted core by hardened walls of polyurethane resin that define solid barriers against the migration of water. This solution to the water migration problem is disadvantageous because it makes the cable heavy and stiff. An additional disadvantage is that, upon bending of the cable, stress may flow from the slotted core to the hardened polyurethane and thence to the optical fibers therein, whereby the optical fibers may experience breakage, macrobending, or microbending.
As noted above, flooding or filling compounds may be used to block the flow of water in a fiber optic cable. U.S. Pat. Nos. 4,752,113 and 4,701,015 disclose a messy and hard to remove polybutylene flooding compound or jelly. Loosely applied damp-proof powder is disposed between spaced masses of the jelly. The loose damp-proof powder is intended to be confined between the spaced masses of jelly, thereby solving a stated problem regarding the non-uniform distribution of the loose powder in the cable due to vibration of the cable during transportation or installation of the cable. This solution to the problem of water migration is disadvantageous because the jelly is messy and hard to remove. An additional disadvantage is that the application of loose powder and spaced masses of jelly hinder manufacturing processes and result in high production costs. Moreover, the jelly material is expensive and it makes the cable heavy and difficult to route through cable passageways.
As noted above, a dry water absorbent chemical is more craft-friendly than hardened resin walls or a hard to remove and messy flooding or filling compound. A typical water absorbent chemical includes a polymer chain with reaction sites that react with water, thereby transforming the water absorbent chemical into an expanded mass of viscous gel. The viscous gel acts as a physical barrier to the migration of water. The water absorbent chemical is typically impregnated in a yarn or a non-woven tape along the full length of the yarn or tape. Such water blocking tapes and yarns may be disadvantageous because they may not be effective to block the flow of water in small chinks, gaps, and spaces of interstices within the cable. Additionally, since the cost to produce a fiber optic cable should be minimized, and the use of water absorbent chemicals contributes to the cost of production, the use of such chemicals should be kept to the minimum necessary to meet specifications.
It is an object of the invention to provide a fiber optic cable comprising a cable core having at least one optical fiber, the cable core including fiber optic cable components that define superficies and interstices of said cable core, at least portions of the fiber optic cable components include at least one water absorbent stripe, the stripe comprising a water absorbent substance for absorbing water and thereby blocking the flow of water in the cable, the stripe coating portions of said cable core.
It is another object of the present invention to provide a fiber optic cable comprising a cable core having at least one optical fiber, the cable core including fiber optic cable components arranged about a longitudinal axis of the cable, the fiber optic cable components defining superficies and interstices of the cable core, portions of the fiber optic cable components include at least one water absorbent stripe, the stripe coating superficies and interstices of the cable core along a generally helical path generally centered about the longitudinal axis of the cable.
It is a further object of the present invention to provide a fiber optic cable comprising a cable core having at least one optical fiber, the cable core including fiber optic cable components arranged about a longitudinal axis of the cable, the fiber optic cable components including respective water absorbent stripes, the fiber optic cable components arranged in the cable core so that respective stripes are transversely aligned with each other, relative to the longitudinal axis, thereby defining water absorbent positions within the cable.
It is an object of the present invention to provide a manufacturing line for the manufacture of at least one fiber optic cable component, the manufacturing line comprising a coating chamber with at least one water absorbent substance nozzle, a fiber optic cable component passing through the chamber adjacent the nozzle, a programmable controller operative to monitor cable component length information via a length sensor, the programmable controller being operative to control the water absorbent substance nozzle to propel the water absorbent substance toward the cable component so that at least portions of the cable component are coated with a water absorbent stripe.
It is another object of the present invention to provide a method of making a fiber optic cable, comprising the steps of monitoring cable component length information, and coating a fiber optic cable component with a stripe comprising a water absorbent substance.